The overall hypothesis addressed by this program is that non- fibrillar aggregated assemblies of amyloid beta (Abeta) which we refer to as Abeta-derived active ligands (ADALs) are active in triggering Alzheimer's disease (AD)-specific cellular responses leading to glial activation, neuronal plasticity malfunction, degeneration and ultimately cell death. We further propose that the generation of these active supramolecular structures of Abeta aggregates can be influenced by the presence of other plaque components, particularly those components derived film glia, and that responses of glial cells contribute to an environment that facilitates and enhances the formation of these bioactive ADALs. It is the goal of this program to isolate and characterize the ADALs examine the conditions that promote their formation, determine the glial and neuronal responses elicited by specific ADALs, and elucidate the interplay of ADAL-glial-neuronal responses. A longer term goal is correlation of bioactive Abeta structures and cellular responses that we characterize in vitro with evidence that these same Abeta structures and responses are associated with pathology in AD brain. Towards these goals, three highly integrated and interactive projects are proposed. Project l will prepare and characterize ADALs structurally, examine the kinetics of ADAL formation (with or without added glial proteins provided by project 2), and determine what factors influence the formation of ADAl-s. The ADAL preps will be provided to Projects 2 and 3 for evaluation of bioactivity on glia and neurons, respectively. Immunohistochemical studies on AD brain tissue will also be done to document whether manifestations of specific molecular events induced by Abeta in glia or neuronal cultures can be detected in AD brain. These cooperative and synergistic interactions among a group of investigators with complementary expertises provide a broad-based, yet focused approach to addressing fundamental mechanistic questions about the processes and pathways involved in generation of AD neuropathology. In addition, our collaborations have led to significant new discoveries about the genesis of neurotoxic amyloid, the influence of glial-derived proteins on amyloid toxicity, and the specific molecular signaling pathways that mediate amyloid Abeta- induced neurodegeneration. These extensive feasibility data suggest a high probability for successful accomplishment of our proposed goals.